This invention relates generally to gas turbine engine nozzles and more particularly, to methods and apparatus for cooling gas turbine engine nozzles.
Gas turbine engines include combustors which ignite fuel-air mixtures which are then channeled through a turbine nozzle assembly towards a turbine. At least some known turbine nozzle assemblies include a plurality of nozzles arranged circumferentially and configured as doublets within the engine downstream from the combustors. A turbine nozzle doublet includes a pair of circumferentially-spaced hollow airfoil vanes coupled by integrally-formed inner and outer bands. The nozzles are cooled by a combination of internal convective cooling and gas side film cooling.
Each nozzle includes a pair of sidewalls that are connected at a leading edge and a trailing edge. The metal temperature distribution of a typical vane airfoil is such that the trailing edge is significantly hotter than the temperature of the bulk of the airfoil. The temperature gradient created results in high compressive stress at the vane trailing edge, and the combination of high stresses and high temperatures generally results in the vane trailing edge being the life limiting location of the nozzle. Accordingly, within at least some known nozzles, the airfoil vane trailing edge is cooled by a film of cooling air discharged from an internally-defined vane cavity. More specifically, the film of cooling air is discharged through trailing edge slots formed on the airfoil vane pressure side, and upstream from the airfoil vane trailing edge.
The amount of air supplied to each nozzle vane is attempted to be optimized to lessen the effect on engine performance decrement that may be associated with cooling flow extraction. Generally, the slots are formed with a length that facilitates optimizing an amount of cooling flow supplied to the trailing edge. Because of the slot length, such slots are typically manufactured using an electrical discharge machining (EDM) process. However, such a manufacturing process may increase manufacturing costs and times, and because of the complexity of the task may cause airfoil vanes to be reworked. A nozzle design including an internal cooling geometry that is compatible with the investment casting process generally is less expensive to manufacture relative to a nozzle design that requires the EDM process to produce the slots.
In one aspect, a method for cooling a turbine nozzle for a gas turbine engine is provided. The nozzle includes an airfoil and the method includes providing an airfoil including a first sidewall and a second sidewall connected at a leading edge and a trailing edge such that a cavity is defined therebetween, the airfoil also including a plurality of pins extending between the first and second sidewalls, and at least one turbulator, the first sidewall including a plurality of slots in flow communication with the airfoil cavity and extending through the first sidewall towards the trailing of the airfoil. The method also includes channeling cooling air into the airfoil cavity such that the airflow is routed through the pins and then through the turbulators before exiting the airfoil through the first sidewall slots.
In another aspect, a turbine nozzle for a gas turbine engine is provided. The nozzle includes a hollow airfoil vane including a first wall, a second wall, and a plurality of pins extending therebetween. The nozzle also includes at least one row of turbulators. The first and second walls are connected at a leading edge and a trailing edge. The first wall includes a plurality of slots extending towards the trailing edge, and the row of turbulators are substantially radially-aligned and extend between the plurality of slot and the pins.
In a further aspect, an airfoil for a gas turbine engine nozzle is provided. The airfoil includes a first sidewall and a second sidewall connected at a trailing edge such that a cavity is defined therebetween. Each sidewall extends radially between an airfoil root and tip. The first sidewall includes a plurality of slots that extend towards the trailing edge. The airfoil also includes a plurality of pins and at least a row of turbulators. The pins extend between the first and second sidewalls, and the turbulators extend between the pins and the slots.